This invention relates to a gauge for measuring the force exerted on a lever, and more particularly to a gauge for measuring the force required to pull a landing gear control lever to an extended position and to pivot the lever to either of its two control positions.
The landing gear on certain commercial airplanes is controlled from the cockpit by a landing gear control lever. This lever is pivotally mounted in the control panel of the cockpit for pivotal movement between a center "off" position, a raised position in which the hydraulic actuators are pressurized to raise or retract the landing gear, and a lowered position in which the hydraulic actuators are pressurized to lower or extend the landing gear. To prevent accidental movement of the landing gear control lever, it is designed to require that the lever be pulled out to an extended position before it can be pivotally moved to either the "up" or "down" position.
To facilitate the easy gripping of the end of the control lever so that it may be pulled to its extended position and then pivoted up or down to either control position, it is provided with a grip roller which is small enough that it does not encumber or clutter the front of the control panel but provides a secure and comfortable grip of the end of the control lever.
One of the quality control procedures for the manufacturing of airplanes is to insure that the force necessary to move the landing gear control lever is within design specifications. This is normally in the range of 7-10 pounds which insures that the lever can be easily and quickly moved when desired but that the force necessary to move the lever is sufficient to prevent its accidental or inadvertent movement by being bumped or the like.
The conventional technique for measuring the force necessary to move the lever used a spring scale which was attached to the end of the lever. The operator pulled on the end of the spring scale while watching the scale indicator to measure the force necessary to move the lever. This technique was inaccurate because the scale would show only momentarily the peak force exerted and required a skilled and experienced operator to obtain data with acceptable reliability. Even more importantly, the control panel of the cockpit in which the lever is installed has adjacent surfaces closely overhanging and underlying the space into which the control lever extends which make it very awkward to position the spring scale in line with the direction of movement of the lever so that the measured force would actually measure the force necessary to be exerted on the lever in the direction of motion.
Measurement precision of the force necessary to move the lever is advantageous not only because of the desire to maintain manufacturing processes within specification, but also because of the information that it reveals about the use of the hydraulic controllers and actuators in the system. The controllers for the actuators are designed to be essentially zero force movement controllers, meaning that the force necessary to move the actuator controller should be near zero. It is most convenient to measure the force necessary to move an actuator controller as installed in a operating system by measuring the force on the control lever, and therefore the instrument for measuring that force must be very precise to reveal the desired information about the controllers in the installed system.
Thus, there has long been a need in the industry for a gauge that will measure the force necessary to move a lever about its pivot point in such a way that the force exerted on the lever can be applied conveniently and quickly in the correct direction despite the confined position in which the lever is mounted. The instrument must be highly accurate and be capable of storing the desired information for reading and recording after the measurement is taken. The instrument should be capable of recording both tension and compression forces since the position of the lever may in some instances require that the force exerted on the lever be a pull and in other instances a push. The instrument should be easily mounted and dismounted from the landing gear control lever and, when mounted, be securely fixed to the lever. Finally, it should be small and light to facilitate its use in a cramped confines of the cockpit, should be inexpensive to manufacture, and be rugged for long use in the factory.